To see a world without heavy metal, an unmetalled world, simply rotate your cranium a few degrees to the right or left. Perhaps you are in Starbucks, where it is time for your Iced Caramel Macchiato. Not a single unnameable beast assaults you as you make your way to the counter. Rounding the display of merchandise, you are neither hexed by depression nor dragged to hell in the arms of a she-demon. You place your order, quite failing to bellow with psychic agony. There is no heavy metal anywhere.

Or is there? For as you wait, drink in hand, at the condiment bar, in the usual muttering press of sugar-grabbers and milk-seekers, you feel a tremendous agitation. You feel, in fact, fleetingly homicidal. Who are these people? Why are they taking so long? If only you could smite them all …

“We seem to move on a thin crust,” warned Sir James George Frazer in The Golden Bough,

which may at any moment be rent by the subterranean forces slumbering below. From time to time a hollow murmur underground or a sudden spirt of flame into the air tells of what is going on beneath our feet.

Though written in 1922, this is metalspeak, pure and simple. The venerable mythographer was presaging not only the basso quakes and pyro-blasts that have long been a staple of the larger metal shows, but the metal mind-set itself. Since its invention (to which we will return in a moment), heavy metal has been the popular music most ardently devoted to Frazer’s underground magma pools, and most grandly expressive of their inevitable eruption. Metal’s commerce with the lower realm has been extravagant, ridiculous, and covered in glory. The sleeper parched of his dreams, or purged of his nightmares, goes swiftly bonkers: without fantasy there is no reality. It might be argued—indeed, it will be argued, by me, right now—that heavy metal has kept us sane.

It’s been 40 years since the release of Black Sabbath’s Master of Reality and 25 since Metallica’s Master of Puppets, the first presenting us with the aboriginal metal vision, the second refining that vision dramatically. And today we find ourselves in something of a metal slump. There’s plenty of it around; the kids, in hundreds of thousands, are buying albums by Disturbed or Avenged Sevenfold; longtime casualties like your correspondent are enjoying Mastodon, High on Fire, and the smoldering Zoroaster; the extremist has his niche metals—his death metal and his black metal and his drone metal and his vocals that sound like a man vomiting in a cathedral. And the hoary old gods (Slayer, Metallica) are still chucking the odd thunderbolt. But metal’s profile is low: the mega-tours seem to pass invisibly from city to city, with no new figureheads arising at whom the general populace can scream and throw turnips. Metal didn’t even dent Billboard’s top 50 best-selling albums of 2010. Prompting the question: Have we passed peak metal?

Unlikely, I think. Metal renews itself, as we shall see. Nonetheless, the moment invites us to cogitate a little upon the whole heavy-metal thing—to go back, as it were, to first principles.

Black Sabbath created heavy metal. We can say that with a satisfying kick-drum thump of certainty. Cream was heavy; Hendrix and Led Zeppelin were heavier still; in Japan, the Flower Travellin’ Band was shockingly heavy; but Black Sabbath, from Birmingham, England, was heavy metal. No joy here, nor any wisp of psychedelic whimsy. From the first note, this band sounded ancient, oppressed, as if shambling forward under supernatural burdens. With his use of horror-movie atmospherics—the tension-building tritone or flatted fifth—and the leering majesty of his riffs, guitarist Tony Iommi redirected the spiritual drag of the blues into an uncharted world of bummers and black holes. Bassist Geezer Butler, a mystical vegetarian, wrote the lyrics. Raised Catholic, Butler as a youngster had entertained thoughts of the priesthood, and for all the band’s occult trappings, his view of things was essentially orthodox, if a little on the medieval side: God over here, Satan over there, man flailing and biting his nails in the middle. “Lord of This World,” from 1971’s Master of Reality, made it all very clear:

Your world was made for you by someone above
But you chose evil ways instead of love
You made me master of the world where you exist
The soul I took from you was not even missed

Relaying these panoramas in a bleak, monastically removed voice was singer Ozzy Osbourne—pre-solo-career, pre-reality-TV. Ozzy was a failed burglar, with meaty, tattooed fingers and the eyes of a worried child, who had once—without quite knowing why—daubed the legend IRON VOID on a roadside wall. Vocally, he filtered Butler’s Boschian sensibility through his own late-20th-century depression, in front of a band almost overloading with musical power: early live footage reveals the musicians “bobbing,” in the superb phrase of the metal historian Ian Christe, like “marionettes in the hands of God.” The sound itself dramatized a violent, existential bottoming-out, Iommi’s guitar lines rearing and plunging across the awesomely delayed crashes of drummer Bill Ward, percussions so far behind the beat that their impact was interior, nearly glandular, like the drench of adrenaline after hearing bad news. Thousands have attempted it, but the Sabbath sound has proved uncannily resistant to imitation: one band might achieve the huge travail of Iommi’s guitar tone, another the weird, weltering swing of the rhythm section. But no one else has managed to do both at once.

Rooted by instinct in the Dark Ages, squintingly at odds with progress, metal nonetheless strode forward hand in hand with technology: distortion, amplification, sustain; speaker stacks rising higher and higher. One well-struck chord, and the concertgoer was twisting in a vibrational abyss. Judas Priest (also founded in Birmingham) made a spectacular fetish of this new power in anthems such as 1980’s “Metal Gods”: “Marching in the streets / Dragging iron feet / Laser beaming hearts / Ripping men apart!” Spiked-and-leathered front man Rob Halford was a shattering diva, taking the stage on a Harley-Davidson and blasting unstoppably through the octaves.

Metal spawned plenty of variants in the ’70s and early ’80s, heavier or lighter in proportion to their distance from Sabbath’s original Weltanschauung—a word I use only because it sounds like a heavy-metal power chord. There was the goofy hedonist-metal of Kiss; the glorious, metallicized boogie of AC/DC; and the zooming, beyond-metal exuberance of Eddie Van Halen. Punk rock arrived, short-haired and anti-fantastical: no longer was it cool to sing about wizards. Still, metal insisted upon its diableries and warrior kings, even as its new standard-bearers (Diamond Head, Iron Maiden) made use of punk’s acceleration. Punk rockers, returning the compliment, commenced to pinch metal riffs.

Against the onslaught of callow modernity and shrinking guitar solos, metal’s treasury was preserved, transmitted, as the monks of old Ireland preserved and transmitted the manuscripts of the pagans. The year 1986 was a metal bonanza. Listen to Motörhead’s “Orgasmatron” on the album of the same name, and the song is a mid-paced rumble-grumble with an unmelodic vocal and a horrible snare sound—by no means the band’s finest hour. But when Motörhead went into the BBC’s studios that year to record a session for radio, lead singer Ian “Lemmy” Kilmister—one of metal’s great survivors—made a wonderful artistic choice: he recited the lyrics, unaccompanied. This is the way to hear “Orgasmatron”—as a poem, uttered in a burned-out, purely English voice (slight Staffordshire accent) that seems to issue from the deepest crevasse of J. R. R. Tolkien’s imagination.

I am the one, Orgasmatron, the outstretched grasping hand
My image is of agony, my servants rape the land …
I twist the truth, I rule the world, my crown is called deceit
I am the emperor of lies, you grovel at my feet

Orgasmatron is religion, politics, war: the dark and many-faced dominator of history, with man his piteous plaything. Now, what could be more heavy metal than that?

Answer: Metallica. The eight-and-a-half-minute title track of Master of Puppets, also released in 1986, is a battering, symphonic piece of speed metal, prodigal in its arrangements but performed in a cold fury of austerity, with nothing of Sabbath’s organic doom-groove. The Lord of This World, the Orgasmatron, the Master of Puppets has found a new matrix through which to work his ends, a new mechanism of despair: addiction.

Metallica’s singer/guitarist James Hetfield—after Geezer Butler, the second great poet of heavy metal—would go on to make more-complex metaphysical statements: the astonishing “Sad But True,” from 1991’s Metallica, is Schopenhauer in the key of E minor. But with “Master of Puppets,” he hit a metal mother lode. Subjugators and string-pullers, principalities and powers: in the face of all these, heavy metal is cosmic protest music.

By dwelling at such length on the lyrics, and mentioning Schopenhauer, I of course risk the capital vice of the writer-on-metal: I risk being intellectual. Nothing disgusts a metalhead more than to be intellectualized. Which is not to say that he himself is without conceit in that department. The metalhead, quite counter to stereotype, is floridly pretentious. He will call his band Sanctum of Carnality, or Thy Maleficence; he will steep himself in the Stygian prose of H. P. Lovecraft, possibly the most insane overwriter since Webster; he will root through his thesaurus to find a fancy word for “dismemberment”; he will make up his own words, heavy-sounding words, like thraft (High on Fire) and cleansation (Chimaira). But all of this is best understood as a kind of voodoo, a force field of metal-ness with which to ward off the triflers and non-tragedians, while simultaneously short-circuiting the apparatus of good taste, correctly identified by the proto-metalhead G. K. Chesterton as “the last and vilest of human superstitions.” Faddists and lightweights: keep your distance. Critic: we will make your brain explode.

Culturally, metal has lost its boogeyman privileges, having been superseded in infamy first by gangsta rap and then by Britney with her shaved head and her dangerous umbrella. Never say never, but it appears that the age of anti-metal litigation is also over—that it peaked in 1990 with the suit against Judas Priest, in which it was alleged that backward messages concealed on the album Stained Class had driven two fans to suicide. This, even more than a similar 1986 suit against Ozzy Osbourne, was metal’s Scopes trial: Priest front man Rob Halford, he of the four-octave range, cracked up the courtroom with a tape of the backward messages he had found in Stained Class, including one that seemed to say, “Hey look, Ma, my chair’s broken.”

The panicking parents of yesteryear now seem like characters from folk memory. An anti-metal case in our current climate might more appropriately be brought by Richard Dawkins or the Council for Secular Humanism, arraigning some metalhead for singing too loudly about damnation. Not every metal act subscribes to the cosmology of Geezer Butler as made manifest in the sound of Black Sabbath: metal today is produced with equal sincerity and efficacy by atheists and Christians, depressives and libertines, diabolists, miserablists, absurdists, and those whose only religion is metal itself. But when it starts to get heavy, dilating your blood vessels and stirring the roots of your hair, you know you are approaching the primary vision—of man besieged, man pulled apart, man suspended over gulfs of penal fire.

Nu metal, the big metal noise of the ’90s and early ’00s, has come and gone. Metalheads never really went for it—too much rapping in there, and not enough warlocks. Where was the dread? The moral-astronomical scale? The itchy, hybrid bounce-crunch of Korn and Limp Bizkit seemed linked less to metal’s traditional concerns than to the blocked ducts and thwarted entitlements of a generation of football players. But even here metal was still performing at least one of its offices, doing bootleg rage therapy for a mass audience: in the moiling and roaring of Korn’s Jonathan Davis, especially, something fundamental seemed to be seeking an outlet. Other bands of the era had more typically metallic preoccupations. Fear Factory was obsessed with technology and the dissolution of the individual: “Must not surrender my God to anyone,” sang Burton C. Bell, “or this body will become carrion!” Slipknot, masked and boilersuited, the maddest of them all, had its fans going about in T-shirts that read People = Shit. Which is, you must admit, succinct.

The great scholar of heavy metal Robert Walser, doing research for his 1993 book, Running With the Devil, interviewed a Twisted Sister fan who told him that the easy-listening music favored by her mother had made her paranoid. In Walser’s words: “It so obviously seems to lie to her about the world.” An Avenged Sevenfold fan might say the same today about the music of Jack Johnson, or John Mayer, or Jason Mraz, or any of the golden troubadours on heavy rotation at your local Starbucks. I don’t mean to be ungracious about Starbucks—I happen to spend a good deal of time in Starbucks—but heavy metal reminds me that Starbucks, like much of modern life, is a fiction. Go through the membrane, break the crust, and everything is metal.